European patent EP 053 76 01, which goes back to the applicant of the present application, discloses a stopper in the head section of which such a slide is arranged. The slide has a recessed grip formed in the upper side, into which a user grips with one finger to push the slide forwards beyond the container rim. The slide in the retracted initial position is held by a projection on the bottom section of the stopper over which the slide can slide without the application of a considerable force. The recessed grip may catch an infant's attention, with the infant pushing the slide out of the head section and then being able to lever off the stopper from the container.